Implantable medical device incorporating performance based adjustable power supply

Abstract

A method or apparatus for conserving power in an implantable medical device (IMD) of the type having at least one IC powered by a battery wherein, in each such IC, a voltage dependent oscillator for providing oscillator output signals at an oscillation frequency dependent upon applied supply voltage to the IC is incorporated into the IC. The voltage dependent oscillator oscillates at a frequency that is characteristic of the switching speed of all logic circuitry on the IC die that can be attained with the applied supply voltage. The applied supply voltage is regulated so that the oscillation frequency is maintained at no less than a target or desired oscillation frequency or within a desired oscillation frequency range. The power supply voltage that is applied to the IC is based directly on the performance of all logic circuitry of the IC. In order to provide the comparison function, the oscillator output signals are counted, and the oscillator output signal count accumulated over a predetermined number of system clock signals is compared to a target count that is correlated to the desired oscillation frequency. The counts are compared, and the supply voltage is adjusted upward or downward or is maintained the same dependent upon whether the oscillator output signal count falls below or rises above or is equal to the target count, respectively. The supply voltage adjustment is preferably achieved employing a digitally controlled power supply by calculating a digital voltage from the comparison of the oscillator output signal count to the target count, and storing the digital voltage in a register of the power supply.

What is claimed is: 
     
       1. Apparatus for conserving power of a battery in an implantable medical device of the type having at least one integrated circuit powered by a supply voltage and current drawn from the battery to operate at an integrated circuit switching speed comprising: a voltage dependent oscillator incorporated into the integrated circuit for providing oscillator output signals at an oscillation frequency dependent upon the supply voltage applied to the integrated circuit;   means for defining a desired oscillation frequency that is correlated to a desired switching speed of all circuitry of the integrated circuit; and   means for regulating the supply voltage to the integrated circuit to maintain the oscillation frequency of the voltage dependent oscillator at the desired oscillation frequency.   
     
     
       2. The apparatus of claim 1, wherein the desired oscillation frequency comprises a desired oscillation frequency range. 
     
     
       3. The apparatus of claim 1, wherein the integrated circuit is formed employing CMOS fabrication techniques into semiconductor elements exhibiting p-channel and n-channel thresholds and the regulating means further comprises: means for regulating the power supply voltage low enough to allow operation of the CMOS semiconductor elements below the sum of the p-channel and n-channel thresholds, which reduces power consumption while maintaining satisfactory switching speed.   
     
     
       4. The apparatus of claim 1, further comprising: wait timer means for inhibiting operation of said first timer means for a wait time following provision of the control signal by said control means to allow said power supply means to adjust said supply voltage to a voltage defined by the control signal.   
     
     
       5. The apparatus of claim 1, wherein the desired oscillation frequency comprises a desired oscillation frequency range and the regulating means further comprises: means for adjusting the supply voltage applied to the integrated circuit;   means for measuring the oscillation frequency and providing a measured oscillation frequency;   means for comparing the measured oscillation frequency to the desired oscillation frequency range;   means for maintaining the supply voltage to the integrated circuit if the measured oscillation frequency falls within the desired oscillation frequency range;   means for increasing the supply voltage to the integrated circuit if the measured oscillation frequency falls below the desired oscillation frequency range; and   means for decreasing the supply voltage to the integrated circuit if the measured oscillation frequency rises above the desired oscillation frequency range.   
     
     
       6. The apparatus of claim 1, wherein the regulating means further comprises: means for adjusting the supply voltage applied to the integrated circuit;   means for measuring the oscillation frequency and providing a measured oscillation frequency;   means for comparing the measured oscillation frequency to the desired oscillation frequency range;   means for maintaining the supply voltage to the integrated circuit if the measured oscillation frequency falls within the desired oscillation frequency range;   means for increasing the supply voltage to the integrated circuit if the measured oscillation frequency falls below the desired oscillation frequency range; and   means for decreasing the supply voltage to the integrated circuit if the measured oscillation frequency rises above the desired oscillation frequency range.   
     
     
       7. A method for conserving power in an implantable medical device of the type having at least one integrated circuit powered by a battery comprising the steps of: (a) forming the integrated circuit with a voltage dependent oscillator for providing oscillator output signals at an oscillation frequency dependent upon applied voltage;   (b) establishing a desired oscillation frequency;   (c) deriving a supply voltage from said battery;   (d) applying the supply voltage to the integrated circuit, thereby causing the voltage dependent oscillator to provide oscillator output signals at an oscillation frequency dependent upon the applied supply voltage;   (e) comparing the oscillation frequency of the oscillator output signals to the desired oscillation frequency;   (f) incrementally increasing the derived supply voltage if the oscillation frequency of the oscillator output signals is less than the desired oscillation frequency and repeating steps (c), (d) and (e);   (g) incrementally decreasing the derived supply voltage if the oscillation frequency of the oscillator output signals is greater than the desired oscillation frequency and repeating steps (c), (d) and (e); and   (h) maintaining the derived supply voltage if the oscillation frequency of the oscillator output signals is equal to the desired oscillation frequency and repeating steps (c), (d) and (e).   
     
     
       8. The method of claim 7, wherein the desired oscillation frequency comprises a desired oscillation frequency range. 
     
     
       9. The method of claim 7, wherein the integrated circuit is formed employing CMOS fabrication techniques into semiconductor elements exhibiting p-channel and n-channel thresholds and the desired oscillation frequency is set to ensure that the derived supply voltage allows operation of the CMOS semiconductor elements below the sum of the p-channel and n-channel thresholds, which reduces power consumption while maintaining satisfactory switching speed. 
     
     
       10. The method of claim 7, further comprising the step of: wait timer means for inhibiting operation of said first timer means for a wait time following provision of the control signal by said control means to allow said power supply means to adjust said supply voltage to a voltage defined by the control signal.   
     
     
       11. Apparatus for conserving power in an implantable medical device of the type having at least one integrated circuit powered by a battery comprising: a voltage dependent oscillator formed on the integrated circuit for providing oscillator output signals at an oscillation frequency dependent upon applied voltage;   means for establishing a desired oscillation frequency;   means for deriving a supply voltage from said battery;   means for applying the supply voltage to the integrated circuit, thereby causing the voltage dependent oscillator to provide oscillator output signals at an oscillation frequency dependent upon the applied supply voltage;   means for comparing the oscillation frequency of the oscillator output signals to the desired oscillation frequency;   means for incrementally increasing the derived supply voltage if the oscillation frequency of the oscillator output signals is less than the desired oscillation frequency;   means for incrementally decreasing the derived supply voltage if the oscillation frequency of the oscillator output signals is greater than the desired oscillation frequency; and   means for maintaining the derived supply voltage if the oscillation frequency of the oscillator output signals is equal to the desired oscillation frequency.   
     
     
       12. The apparatus of claim 11, wherein the integrated circuit is formed employing CMOS fabrication techniques into semiconductor elements exhibiting p-channel and n-channel thresholds and the desired oscillation frequency is set to ensure that the derived supply voltage allows operation of the CMOS semiconductor elements below the sum of the p-channel and n-channel thresholds, which reduces power consumption while maintaining satisfactory switching speed. 
     
     
       13. Apparatus for conserving power in an implantable medical device of the type having at least one integrated circuit powered by a battery comprising: a voltage dependent oscillator formed on the integrated circuit for providing oscillator output signals at an oscillation frequency dependent upon applied voltage;   power supply means responsive to a control signal for deriving a supply voltage from said battery and applying the supply voltage to the integrated circuit, thereby causing the voltage dependent oscillator to provide oscillator output signals at an oscillation frequency dependent upon the applied supply voltage;   first counter means for counting oscillator output signals and accumulating an oscillator signal count over a predetermined time period; and   control means for comparing the oscillator signal count accumulated over the predetermined time period to a desired oscillator signal count representing a desired oscillation frequency of said voltage dependent oscillator and for providing the control signal to the power supply means as a function of the comparison.   
     
     
       14. The apparatus of claim 13, wherein the control means provides said control signal for incrementally increasing the supply voltage if the accumulated oscillator signal count is less than the desired oscillator signal count indicating that the oscillation frequency of the oscillator output signals is less than the desired oscillation frequency. 
     
     
       15. The apparatus of claim 13, wherein the control means provides said control signal for incrementally decreasing the supply voltage if the accumulated oscillator signal count is greater than the desired oscillator signal count indicating that the oscillation frequency of the oscillator output signals is greater than the desired oscillation frequency. 
     
     
       16. The apparatus of claim 13, wherein the control means provides said control signal for maintaining the supply voltage if the accumulated oscillator signal count is equal to the desired oscillator signal count indicating that the oscillation frequency of the oscillator output signals is equal to the desired oscillation frequency. 
     
     
       17. The apparatus of claim 13, further comprising: means for providing a system clock signal, the frequency of which is independent of supply voltage; and   second counter means for counting system clock signals; and wherein: said control means further comprises means for comparing the oscillator signal count accumulated in the first counter means over the predetermined time period comprising one or more system clock signals counted in said second counter means.     
     
     
       18. The apparatus of claim 13, further comprising: wait timer means for inhibiting operation of said first timer means for a wait time following provision of the control signal by said control means to allow said power supply means to adjust said supply voltage to a voltage defined by the control signal.   
     
     
       19. The apparatus of claim 13, wherein the integrated circuit is formed employing CMOS fabrication techniques into semiconductor elements exhibiting p-channel and n-channel thresholds and the desired oscillation frequency is set to ensure that the derived supply voltage allows operation of the CMOS semiconductor elements below the sum of the p-channel and n-channel thresholds, which reduces power consumption while maintaining satisfactory switching speed.